Transmission and vehicle using same

ABSTRACT

A vehicle provided with an engine  1  which generates a driving energy for the vehicle, planetary gears  4  and  6  comprising sun gears, planet gears and ring gears, motors  8  and  9  for respectively controlling the sun gears, and a clutch  14,  the planet gears being connected to an input shaft driven by the engine and the ring gears connected to an output shaft for driving wheels, wherein gear ratios from the input shafts to the output shafts in the planetary gears  4  and  6  are set at a value different to each other. A stepless speed changing function which permits vehicular operation in a high engine efficiency region while minimizing an electrical energy loss is realized by a small-sized transmission using small-sized motors. The vehicle, which uses the transmission, can be operated in a high engine efficiency region while keeping an electrical energy loss to a minimum.

TECHNICAL FIELD

[0001] The present invention relates to a transmission comprising motorsand differential mechanisms, as well as a vehicle using the same.

BACKGROUND ART

[0002] As a drive system capable of reducing the fuel consumption of anengine there is known a hybrid vehicle which utilizes a motor driveforce.

[0003] Various types of hybrid vehicles such as series type and paralleltype have been proposed, among which is included a series-parallelhybrid type using two motors and one planetary gear. For example, inJapanese Patent Laid-open No. Hei 7-135701 there is disclosed a methodwherein a driving force of an engine is inputted to a planetary gear andcontrol is made by a generator so that a vehicle is driven with adriving force obtained from an output shaft of the planetary gear. Whilea part of energy of the engine is generated by a generator, a drivingforce is assisted from a motor connected to the output shaft to drivethe engine always in a high torque region of a high efficiency, and atthe same time a speed change function can be attained.

[0004] The same principle as above is also described in Japanese PatentLaid-open Nos. Sho 49-112067 and Sho 58-191364.

[0005] According to the methods disclosed therein, power is generated bya generator and a driving force is obtained by a motor for realizing aspeed change function, so that there occurs an electrical energy loss.Consequently, there occurs reduction in efficiency by an amountcorresponding to the electrical energy loss with respect to the whole ofthe vehicle concerned despite the engine can be driven always at ahighly efficient operating point.

[0006] The present invention has been accomplished in view of theabove-mentioned problems and it is the first object of the invention toprovide a small-sized transmission constituted by small-sized motors,thereby realizing a stepless speed change function which permitsvehicular operation in a region of a high engine efficiency whileminimizing an electrical energy loss.

[0007] It is the second object of the present invention to provide avehicle capable of being driven in a region of a high engine efficiencywhile minimizing an electrical energy loss.

DISCLOSURE OF THE INVENTION

[0008] The above first object of the present invention is achieved by atransmission having a plurality of differential mechanisms in whichmotors control a difference in the number of revolutions between aninput shaft and an output shaft thereof, the input and output shafts forthe plural differential mechanisms being used in common, wherein gearratios from the input shafts to the output shafts in the pluraldifferential mechanisms are set at a value different to each other, andgear ratios from the input shafts to the motors in the pluraldifferential mechanisms are set at a value different to each other.

[0009] Particularly, this construction is effective in reducing the sizeof the motor which controls the differential mechanism smaller in thegear ratio from the input shafts to the output shafts.

[0010] The above first object is achieved also by a transmission havinga plurality of differential mechanisms in which motor shafts driven bymotors control a difference in the number of revolutions between aninput shaft and an output shaft thereof, the input and output shafts forthe plural differential mechanisms being used in common, wherein gearratios from the input shafts to the output shafts in the pluraldifferential mechanisms are set at a value different to each other, thetransmission further having a locking/unlocking mechanism for lockingand unlocking the motor shaft in at least the differential mechanismlarger in the gear ratio of the plural differential mechanisms.

[0011] According to this construction it is possible to reduce the sizeof the motor disposed on the side where the locking/unlocking mechanismis provided. Thus, by using both means described above in combination itis made possible to provide a transmission still smaller in size.

[0012] The above second object of the present invention is achieved by avehicle having an engine which generates a driving energy for drivingthe vehicle and a transmission which changes the rotational speed of theengine and transmits a driving force to wheels, the transmission havingat least first and second differential mechanisms which input thedriving force from the engine and output a driving force for the wheels,and also having first and second motors for controlling the first andsecond differential mechanisms, respectively, wherein gear ratios frominput shafts to output shafts in the first and second differentialmechanisms are set at a value different to each other and gear ratiosfrom the input shafts to the first and second motors are set at a valuedifferent to each other.

[0013] The above second object of the present invention is achieved alsoby a vehicle having an engine which generates a driving energy fordriving the vehicle and a transmission which changes the rotationalspeed of the engine and transmits a driving force to wheels, thetransmission having at least first and second differential mechanismswhich input the driving force from the engine and output a driving forcefor the wheels, and also having first and second motors for controllingthe first and second differential mechanisms, respectively, wherein agear ratio from an input shaft to an output shaft in the firstdifferential mechanism is set at a value larger than a gear ratio froman input shaft to an output shaft in the second differential mechanism,the transmission further having a locking/unlocking mechanism forlocking and unlocking a motor shaft which transmits the driving force ofat least the first motor to the first differential mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a construction diagram of a hybrid vehicle according toan embodiment of the present invention which realizes a speed changefunction with use of two planetary gears whose sun gears are controlledby motors.

[0015]FIGS. 2A and 2B are speed-torque characteristic diagrams of motors8 and 9 shown in FIG. 1.

[0016]FIGS. 3A and 3B are speed-torque characteristic diagrams of motors8 and 9 with a clutch 14 omitted in FIG. 1 and with the same gear ratioon an input side.

[0017]FIG. 4 is a control flowchart for the hybrid vehicle shown in FIG.1.

[0018]FIG. 5 is a control flowchart for the motor 8 and clutch 14 shownin FIG. 4.

[0019]FIG. 6 is a processing flowchart with a trouble occurring in theclutch 14 shown in FIG. 4.

[0020]FIG. 7 is a construction diagram of a hybrid vehicle according toanother embodiment of the present invention wherein input and outputgears of a planetary gear 4 are constructed in a manner different fromthat in FIG. 1.

[0021]FIG. 8 is a construction diagram of a hybrid vehicle according toa further embodiment of the present invention wherein a sun gear 4 s isused on an input side of a planetary gear 4.

[0022]FIG. 9 is a construction diagram of a hybrid vehicle according toa still further embodiment of the present invention wherein the numberof constituent gears is decreased.

[0023]FIG. 10 is a processing flowchart showing a further embodiment ofthe control processing illustrated in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] An embodiment of the present invention will be described belowwith reference to FIG. 1.

[0025]FIG. 1 illustrates an automobile wherein, with use of energy of anengine 1, tires 3 a and 3 b are rotated through drive shafts 2 a and 2 bto drive a body of the automobile. Planetary gears 4 and 6, which areimportant components in the present invention, respectively comprise sungears 4 s and 6 s, planetary gears 4 p and 6 p, and ring gears 4 r and 6r. The sun gears 4 s and 6 s are driven respectively by motors 8 and 9which are controlled by power converters 10 and 11, respectively. As amotor for an automobile, a permanent magnet synchronous motor is mostsuitable from the standpoint of attaining a high efficiency and a smallsize. A battery 12 is used for the supply of energy required by themotors 8 and 9 and for the storage of energy generated by the motors.Rotation of the engine 1 is transmitted to the planet gear 6 p of theplanetary gear 6 via gears 15, 16 and 17 and is also transmitted to theplanet gear 4 p of the planetary gear 4 via gears 19 and 20 which areconnected to the gears 16. Thus, the driving torque of the engine 1 isdistributed to the planetary gears 4 and 6 by the construction from thegear 15 to the gear 20. What is important in the present invention isthat a gear ratio from the gear 15 to the gear 17 and that from the gear15 to the gear 20 are different from each other. As to the operationconcerned, the details thereof will be described later.

[0026] Also as to the ring gears, gears different in gear ratio aredisposed on the output side. A gear 21 is connected to the ring gear 4 rto rotate a gear 5, while a gear 18 is connected to the ring gear 6 r torotate a gear 7. The gears 5 and 7 are clamped to each other and thetires 3 a and 3 b are driven with a torque transmitted from both gears.A gear ratio from the gear 15 located on the input side to the gear 5 onthe output side via the planetary gear 4, which gear ratio means theratio of a rotation cycle of the gear 5 to that of the gear 15 in alocked state of the sun gear 4 s and will hereinafter be referred to asgear ratio L, is set at a value larger than a gear ratio (gear ratio Hhereinafter) from the gear 15 to the gear 7 via the planetary gear 6.Generally, it is desirable to set the gear ratio L at a value three tosix times as large as the gear ratio H. Particularly when thetransmission of the invention is applied to an automobile, it isdesirable to set the gear ratio L at a value four to five times as largeas the gear ratio H, which value is advantageous to the improvement ofthe vehicular driving performance and the reduction in size of thetransmission.

[0027] A description will now be given of one method for driving thevehicle with use of a controller 23 shown in FIG. 1. The control unit 23makes control so that when the vehicle is driven at a low speed and alow torque, the clutch 14 is engaged and a locking/unlocking device 13is released, thereby permitting the vehicle to be driven with a torqueof the motors 8 and 9. By a cooperative speed control with both motors 8and 9 the vehicle is driven while keeping the engine speed ωe zero. Whenthe driver presses down on an accelerator to accelerate the vehicle, theengine 1 is rotated up to a startable speed and is started by acooperative speed control of both motors 8 and 9 so as to permit ahigh-torque drive. After start-up of the engine 1, the motor 9 isbrought into a free running condition, while the motor 8 is lockedelectrically. As a result, the vehicle comes to be driven at the gearratio L from the gear 15 to the gear 5 and therefore a driving force ofhigh speed and high torque can be generated in the tires 3 a and 3 b.This speed change ratio can be regarded as being equal to that of a lowgear in a manual transmission.

[0028] When the vehicle is to be driven by the engine 1 while running ata medium or higher speed, the motor 8 is brought into a free runningcondition electrically, while the motor 9 is locked electrically and isthereafter locked mechanically by the locking/unlocking device 13. As aresult, the vehicle is driven at the gear ratio H from the gear 15 tothe gear 7. Therefore, the engine 1 operates in a low speed, high torqueregion and a change in speed is made to a high speed side by thetransmission to drive the vehicle. In this steady state the engine 1operates in a high efficiency region of a high torque. Besides, sincethe electrical energy is not utilized by the motors 8 and 9, there is noelectrical loss and the vehicular running distance can be made longer ata low fuel consumption. When the vehicle is to be accelerated whilerunning at a medium or higher speed, the motor 8 is brought into adriving condition and the motor 9 into a driving or power generatingcondition to attain the same function as in a continuously variabletransmission or there can be attained a function of adding motorassisting torque to the engine drive force as in a hybrid automobile.

[0029] In the case where the vehicle speed exceeds a predetermined speedin a high-speed running, a control is made to release the clutch 14. Ifthe motor 9 is locked, the motor 8 will be rotated at a high speed,which is therefore prevented by releasing the clutch 14. If a permanentmagnet synchronous motor suitable for an automobile is used as the motor8, an excessive counter electromotive force is generated by a high-speedrotation. Since an excessive counter electromotive force will result indestruction of the power converters, so it is necessary to make a designwhile paying attention to this point. In designing a motor so as toprevent the generation of an excessive counter electromotive force thereis adopted a method wherein the number of turns of winding is madesmall, while an electric current to be passed through the winding isenhanced to ensure a required torque. By adopting such a high-speedrotation preventing construction as in this embodiment it is possible tomake a motor design with a larger number of turns of winding. Thus, inthis embodiment it is possible to make the electric current flowing inthe motor 8 small and therefore it is possible to attain the reductionin size of the motor 8 and in capacity of the power converter 10 fromthe standpoint of a thermal design.

[0030] Setting the gear ratio from the gear 15 to the gear 17 smallerthan the gear ratio from the gear 15 to the gear 20 is advantageous incarrying out the above operations. This point will now be described. Thegear ratio L from the gear 15 to the gear 5 is set several times largerthan the gear ratio H from the gear 15 to the gear 7. Besides, the gears5 and 7 are coupled together through a common shaft.

[0031] If both gear ratios are set at the same value, the motor 9 comesto operate in a narrow speed range relative to the speed range of themotor 8. In view of this point, if the gear ratio from the gear 15 tothe gear 17 is set smaller than the gear ratio from the gear 15 to thegear 20, the maximum operating speed of the motor 9 becomes high, sothat the maximum torque of the motor 9 can be kept small and thus thesize of the motor 9 can be reduced by changing the gear ratios. Since inthis embodiment the gear ratio from the planet gear 4 p in the planetarygear 4 to the motor 8 and the gear ratio from the planet gear 6 p in theplanetary gear 6 to the motor 9 are the same, the above descriptioncovered only the components up to the input portions of the planetarygears.

[0032]FIGS. 2A and 2B show speed-torque characteristics (N-Tcharacteristics) of the motors 8 and 9 both used in the embodiment ofFIG. 1. For comparison, FIGS. 3A and 3B show speed-torquecharacteristics of both motors obtained without using the clutch 14 inFIG. 1 and with the gear ratio from the gear 15 to the gear 17 and thatfrom the gear 15 to the gear 20 set equal to each other. With the clutch14, the motor 8 exhibits such a characteristic as shown in FIG. 2A inwhich a high speed region is cut in comparison with FIG. 3A, thuspermitting a motor design so as to increase the number of turns ofwinding and decrease the motor current, whereby the motor 8 and thepower converter 10 can be reduced in size. In comparison with thecharacteristic shown in FIG. 3B, the characteristic shown in FIG. 2Bindicates that the maximum torque of the motor 9 can be diminished. Thisis effective in reducing the size of the motor 9. As a matter of course,that the maximum torque of the motor 9 can be made small leads to adecrease of the motor current, thus permitting the reduction in size ofthe power converter 11.

[0033]FIG. 4 is a flowchart showing a control method for the system ofFIG. 1 in which the control is made by the control unit 23. In step 101in FIG. 4, the control unit 23 inputs operation commands intended by thevehicular driver such as an accelerator depression quantity Xa, a brakedepression quantity Xb, and a change-over signal Xc which instructsforward, reverse, or neutral, as well as vehicular conditions such asvehicle velocity ωv, charging condition of the battery 12, andtemperatures of various components. In step 102, the control unit 23judges whether the clutch 14 is in normal condition or not on the basisof a signal provided from a failure detector 24 shown in FIG. 1. If theanswer is affirmative, there are performed normal control operationsfrom step 103 to step 107, while if the answer is negative, a clutchtrouble processing is executed in step 108. As to the contents of theprocessing performed in step 108, it will be described later withreference to FIG. 6.

[0034] When the clutch 14 is judged to be normal, processings areperformed successively from step 103. In step 103, a vehicular drivingforce command value τr is calculated on the basis of information valuesindicative of vehicle conditions and operation commands which wereinputted in step 101. Next, in step 104, a decision is made as to inwhat manner the driving forces of the engine 1 and motors 8, 9 are to bedistributed, including which of opening and closing commands for theclutch 14 is to be issued, on the basis of the vehicular driving forcecommand value τr and the vehicle velocity ωv. As a result there aredetermined drive command values (torque or speed command values). Instep 105, an engine control calculation is conducted on the basis of adriving force command value for the engine 1 and the engine iscontrolled to satisfy the driving force command value. In step 106, amotor control calculation is conducted on the basis of a driving forcecommand value for the motor 9 and a predetermined driving force isgenerated. Further, in step 107, a control is made to satisfy a drivingforce command value for the motor 8. In this case, it is necessary thatthe processing should include the control for the clutch 14, and thedetails of this processing are shown in FIG. 5. As noted in the previousoperational description in connection with FIG. 1, it is when thevehicle speed exceeds a predetermined value that the clutch should bereleased. Even if the clutch is released when the motor rotating speedexceeds a predetermined value, instead of using the vehicle speed, therewill be obtained an equivalent effect. Even when the torque commandvalue of the motor 8 is zero, if a command for releasing the clutch 14is given, it is possible to diminish a mechanical loss caused byfollow-up rotation of the motor.

[0035] In FIG. 5, the present state of the clutch 14 is judged in step111, and if the clutch is engaged, the processing of step 112 isperformed, while if the clutch is released, the processing of step 116is conducted. In step 112, if a command issued for the clutch 14 is anengaging command, it suffices for the clutch to be kept engaged, so acontrol processing is performed to give a driving force command for themotor 8 in step 113. If the command for the clutch 14 is a releasecommand in step 112, a processing for releasing the clutch is carriedout in step 114. Next, in step 115 the control for the motor 8 isstopped since the clutch 14 is released.

[0036] If the present state of the clutch 14 is a released state, ashift is made from step 111 to step 116, in which a judgment is madeabout a command value for the clutch 14. If the command is a clutchrelease command, a processing is performed to stop the control for themotor 8 in step 115 because it suffices for the clutch 14 to be keptreleased. If the clutch command is an engaging command in step 116, aneven speed control is made for the motor 8 in step 117 so that therotational speed of the motor 8 is made coincident with that of the sungear 4 s. Next, in step 118 there is made judgment as to whether thespeed control has been completed or not in step 118, and only when thespeed control has been completed, a processing for engaging the clutch14 is performed in step 119. The driving force from the motor 8 iscontrolled by performing the above processings.

[0037] The clutch trouble processing method shown in FIG. 4 will now bedescribed with reference to the flowchart of FIG. 6. In step 121 it isdetermined whether the clutch 14 is improperly engaged or not. If theclutch is found to be improperly engaged, a processing is made in step122 to limit a maximum torque capable of being generated by the vehicle.The maximum torque is transferred from the engine 1 and the motor 8 viathe planetary gear 4, but in the case where the clutch 14 cannot beengaged, the torque generated from the engine 1 and the motor 9 istransferred via the planetary gear 6 alone and serves as a drivingtorque for driving the vehicle. Thus, a limitation is made on themaximum torque capable of being generated from gear ratio settingconditions. Therefore, it is notified to the vehicle driver that themaximum torque is limited, and at the same time a processing isperformed to also limit the torque command value. If the clutch 14 isproperly engaged, a processing is made in step 123 to cancel thelimitation on the maximum torque.

[0038] Next, in step 124 it is judged whether the clutch 14 isimproperly released or not, and if the clutch is improperly released,there are performed processings from step 125 to step 127. In step 125 aprocessing is made to limit the maximum vehicle speed. It is assumedthat the limited maximum speed is not higher than the vehicle speedobtained when the motor speed shown in FIG. 2A exceeds 1. Next, in step126, the control for the motor 8 is stopped, and in step 127 a controlfor the engine 1 and the motor 9 is executed within limited speed rangeand torque range. By performing such processings the power converter 10can be prevented from being damaged by a counter electromotive force ata high-speed rotation in an improperly released condition of the clutch14. On the other hand, if it is judged in step 124 that the clutch 14 isproperly released, the limitation on the maximum speed is cancelled instep 128, then in step 129 a control for the engine 1 and motors 8, 9 ismade in a limited state of the maximum torque.

[0039] Thus, according to this embodiment it is possible to provide atransmission of small size and low cost possessing a stepless speedchanging function and a motor assisting function. Besides, thistransmission is applicable not only to ordinary types of automobiles butalso to hybrid automobiles. Although the method adopted in thisembodiment is limiting the maximum vehicle speed, the same effect asabove can also be obtained even by adopting a method of limiting themaximum engine speed.

[0040]FIG. 7 illustrates another embodiment of the present inventionwhich is different from the embodiment shown in FIG. 1 in point of howto construct gears in an automobile. More specifically, the constructionshown in FIG. 7 is different from the construction shown in FIG. 1 in amethod of connecting gears of a planetary gear 4 on input and outputsides. In FIG. 7, a gear 20 meshing with an input-side gear 19 isconnected to a ring gear 4 r in a planetary gear 4. Further, a gear 21engaged with a planet gear 4 p is connected to an output-side gear 5.Thus, the gears of the planetary gear 4 connected to input and outputsides in FIG. 7 are reverse to those in FIG. 1. Since the gear ratiofrom the ring gear to the planet gear in the planetary gear is largerthan 1.0, the gear ratio from the gear 15 to the gear 20 and that fromthe gear 21 to the gear 5 can be set smaller than in FIG. 1.

[0041] It has been described previously that in the embodiment shown inFIG. 1 the gear ratio L from the gear 15 to the gear 5 is set at a valueseveral times larger than the gear ratio H from the gear 15 to the gear7. If the same setting is made in the embodiment shown in FIG. 7, thegear ratios on input and output sides of the planetary gear 4 can bemade closer to the gear ratios on input and output sides of theplanetary gear 6. Consequently, the gears can be designed more easilyand can be arranged in a compact form, thus permitting the realizationof a transmission smaller in size.

[0042]FIG. 8 illustrates a further embodiment of the present inventionwhich is different in how to construct gears from the embodiment shownin FIG. 7. This embodiment is characteristic in that a gear 15 is inmesh with a gear 17 and that the gear 17 is engaged with a planet gear 6p and also with a sun gear 4 s in a planetary gear 4. It is a planetgear 4 p in the planetary gear that is connected to a motor 8 through aclutch 14, with a ring gear 4 r being connected to an output-side gear 5through a gear 22 which is for reverse rotation. The gear ratio from thesun gear 4 s in the planetary gear 4 to the planet gear 4 p is usuallyseveral times larger than the gear ratio from the ring gear 4 r to theplanet gear 4 p. Therefore, by connecting the gear 17 to the sun gear 4s it is possible to obtain a larger gear ratio than in the embodimentsillustrated in FIGS. 1 and 7 and hence possible to omit the gears 16, 19and 20 used in those previous embodiments. As a matter of course, theeffect of reducing the motor size by setting the gear ratios on theinput side of the two planetary gears in FIG. 1 at different values canalso be obtained in the embodiment illustrated in FIG. 8. In theplanetary gear 4, since the rotational direction of the sun gear 4 s andthat of the ring gear 4 r rotated thereby are opposite to each other,the gear 22 is used to obtain a reverse rotation. As a result, uponoperation of the engine 1, the rotation of the gear 5 and that of thegear 7 become coincident with each other within the usual speed range ofeach motor.

[0043] Thus, according to this embodiment it is possible to decrease thenumber of gears used and hence it is possible to realize a more compacttransmission.

[0044]FIG. 9 illustrates an automobile using a still smaller number ofgears according to a further embodiment of the present invention. Sincea basic method for constructing planetary gears is the same as in thesystem of FIG. 7, a description will now be given while makingcomparison with FIG. 7. A rotating shaft of an engine 1 is connected toa planet gear 6 p in a planetary gear 6 and causes a gear 21 to rotatevia a gear 15. The gear 21 is engaged with a ring gear 4 r in aplanetary gear 4. This construction corresponds to the construction ofFIG. 7 in which the gear ratio from the gear 15 to the gear 17 is set at1.0. The gear ratio from the gear 15 to the gear 20 in FIG. 9corresponds to the gear ratio from the gear 15 to the gear 20 in FIG. 7.Thus, equal characteristics can be obtained by making these set valuescoincident with each other.

[0045] In this embodiment, a ring gear 6 r in the planetary gear 6outputs a torque to a gear 7 via a gear 18 which is engaged with thering gear 6 r. The planetary gear 4 is connected to the same shaft asthat of the gear 7 through a planet gear 4 p. A driving torque isoutputted from this shaft to tires 3 a and 3 b. Thus, also as to theoutput-side construction of the planetary gears, the construction shownin FIG. 9 can be made corresponding to the construction shown in FIG. 7.More specifically, the gear ratio from the gear 18 to the gear 7 in FIG.9 corresponds to the gear ratio from the gear 18 to the gear 7 in FIG.7, and if the gear ratio from the gear 21 to the gear 5 in FIG. 7 is setat 1.0, this construction is equal to that shown in FIG. 9.

[0046] In this way a similar performance to that in FIG. 7 can beattained by a system configuration with a smaller number of gears andthus this embodiment is characteristic in that a hydbrid automobilecapable of attaining a speed changing function at low cost can berealized.

[0047]FIG. 10 shows another example of the clutch trouble processingmethod shown in FIG. 4, which is different from that shown in FIG. 6.This processing method is different from that of FIG. 6 in that step 130is provided instead of steps 125 and 126 in FIG. 6. The processing ofstep 130 is performed when the clutch 14 is not properly released. Inthis case, a field weakening control is conducted for the motor 8.According to this field weakening control, a field magnet generated bythe permanent magnet of the motor 8 as a permanent magnet synchronousmotor is cancelled to some extent by the motor current. With thiscontrol, even if the motor 8 is rotated at a high speed, there is nofear that a counter electromotive force may become excessive, because ofa substantial decrease of magnetic flux. Thus, even if the maximumvehicle speed is not limited, there is no fear of damage to the powerconverter 10, so that the driving performance in clutch failure can beimproved.

[0048] Transmissions using two planetary gears controlled by motors andhybrid vehicles using the same, both embodying the present invention,have been described above. The present invention is also applicable tothe case where three or more planetary gears are used, so that a stillmore steps of a transmission can also be constituted. Although themotors referred to above are mainly synchronous motors using a permanentmagnet, there may be used a DC motor using a permanent magnet as a fieldmagnet. The present invention is further applicable to the case where apermanent magnet-free induction motor or synchronous motor is used. Itgoes without saying that a combination of the motors referred to abovecan also be used effectively. Although the control method describedabove mainly control the sun gear in each planetary gear with a motor,there may be adopted another method controlling another gear. Thus, thepresent invention can be practices using any of various combinedmethods. As to the differential mechanisms, planetary gears are used inthe above embodiments, they may be substituted by commonly-useddifferential gears, or when importance is attached to quietness, theremay be used harmonic gears. It is needless to say that the transmissionaccording to the present invention is applicable not only to automobilesbut also to ships and various other vehicles, including rolling stockand bicycles.

[0049] In the present invention, there are used a plurality ofdifferential mechanisms in which motors control a difference in thenumber of revolutions between an input shaft and an output shaftthereof, the input and output shafts for the plural differentialmechanisms being used in common, gear ratios from the input shafts tothe output shafts in the plural differential mechanisms are set at avalue different to each other, and gear ratios from the input shafts tothe motors of the plural differential mechanisms are set at a valuedifferent to each other, whereby it is possible to provide atransmission having a small-sized motor of a low torque and a motorprevented from high revolution and having a stepless speed changingfunction which permits operation in a high engine efficiency regionwhile minimizing an electrical energy loss.

[0050] According to the present invention, in another aspect thereof,there are used a plurality of differential mechanisms in which motorshafts driven by motors control a difference in the number ofrevolutions between an input shaft and an output shaft thereof, theinput and output shafts for the plural differential mechanisms beingused in common, gear ratios from the input shafts to the output shaftsin the plural differential mechanisms are set at a value different toeach other, and there is provided a locking/unlocking mechanism forlocking and unlocking the motor shaft in a differential mechanism whichis larger at least in its gear ratio, whereby there can be provideed atransmission having a small-sized motor of a low torque and a motorprevented from high revolution and having a stepless speed changingfunction which permits operation in a high engine efficiency regionwhile minimizing an electrical energy loss.

[0051] According to the present invention, in a further aspect thereof,in a vehicle having an engine which generates a driving energy fordriving the vehicle and a transmission which changes the rotationalspeed of the engine and transmits a driving force for wheels, thetransmission is provided with at least first and second differentialmechanisms which input a driving force generated by the engine and whichoutput a driving force for the wheels, and is also provided with firstand second motors for controlling the first and second differentialmechanisms, respectively, wherein gear ratios from the input shafts tothe output shafts in the first and second differential mechanisms areset at a value different to each other and gear ratios from the inputshafts to the first and second motors are also set at a value differentto each other. With this construction it is possible to provide avehicle of a low cost and a reduced fuel consumption.

[0052] According to the present invention, in a still further aspectthereof, in a vehicle having an engine which generates a driving energyfor driving the vehicle and a transmission which changes the rotationalspeed of the engine and transmits a driving force to wheels, thetransmission is provided with at least first and second differentialmechanisms which input a driving force generated by the engine and whichoutput a driving force for the wheels, and is also provided with firstand second motors for controlling the first and second differentialmechanisms, respectively, wherein a gear ratio from the input shaft tothe output shaft in the first differential mechanism is set at a valuelarger than a gear ratio from the input shaft to the output shaft in thesecond differential mechanism, and there is provided with alocking/unlocking mechanism for locking and unlocking a motor shaftwhich transmits the driving force of at least the first motor to thefirst differential mechanism. Also with this construction it is possibleto provide a vehicle of a low cost and a reduced fuel consumption.

1. A transmission including a plurality of differential mechanisms inwhich motors control a difference in the number of revolutions betweenan input shaft and an output shaft thereof, said input shaft and saidoutput shaft for said plural differential mechanisms being used incommon, wherein gear ratios from said input shafts to said output shaftsin said plural differential mechanisms are set at a value different toeach other, and gear ratios from said input shafts to the motors in saidplural differential mechanisms are set at a value different to eachother.
 2. A transmission including first and second planetary gears eachcomprising at least three components of a sun gear, a planet gear and aring gear; first and second motors for respectively controlling the sungears in said first and second planetary gears; input shafts connectedto the planet gears in said first and second planetary gears; and outputshafts connected to the ring gears in said first and second planetarygears; wherein gear ratios from said input shaft to said first andsecond motors are set at a value different to each other.
 3. Atransmission including first and second planetary gears each comprisingat least three components of a sun gear, a planet gear and a ring gear:first and second motors for respectively controlling the sun gears insaid first and second planetary gears; input shafts connected to thering gears in said first and second planetary gears; and output shaftsconnected to the planet gears in said first and second planetary gears;wherein gear ratios from said input shafts to said first and secondmotors are set at a value different to each other.
 4. A transmissionincluding an input shaft which inputs a driving force; an output shaftwhich outputs a driving force; first and second planetary gears eachcomprising a sun gear, a planetary gear and a ring gear; and first andsecond motors for respectively controlling the sun gears in said firstand second planetary gears; wherein the planet gear in said firstplanetary gear and the ring gear in said second planetary gear areconnected to said input shaft, while the ring gear in said firstplanetary gear and the planet gear in said second planetary gear areconnected to said output shaft.
 5. A transmission including a pluralityof differential mechanisms in which motor shafts driven by motorscontrol a difference in the number of revolutions between an input shaftand an output shaft thereof, said input shaft and said output shaft forsaid plural differential mechanisms being used in common, wherein gearratios from said input shafts to said output shafts in said pluraldifferential mechanisms are set at a value different to each other, andthere is further included a locking/unlocking mechanism for locking andunlocking the motor shaft in at least a differential mechanism of alarger gear ratio of said plural differential mechanisms.
 6. A vehicleincluding an engine which generates a driving energy for driving thevehicle and a transmission which changes the rotational speed of saidengine and transmits a driving force to wheels, said transmissionincluding at least first and second differential mechanisms which inputa driving force generated by said engine and which output a drivingforce for the wheels, and first and second motors for respectivelycontrolling said first and second differential mechanisms, wherein gearratios from input shafts to output shafts in said first and seconddifferential mechanisms are set at a value different to each other, andgear ratios from said input shafts to said first and second motors areset at a value different to each other.
 7. A vehicle including an enginewhich generates a driving energy for driving the vehicle and atransmission which changes the rotational speed of said engine andtransmits a driving force to wheels, said transmission including atleast first and second differential mechanisms which input a drivingforce generated by said engine and which output a driving force for thewheels, and first and second motors for respectively controlling saidfirst and second differential mechanisms, wherein a gear ratio from aninput shaft to an output shaft in said first differential mechanism isset at a value larger than a gear ratio from the input shaft to theoutput shaft in said second differential mechanism, and there is furtherincluded a locking/unlocking mechanism for locking and unlocking a motorshaft which transmits a driving force of at least said first motor tosaid first differential mechanism.
 8. A vehicle according to claim 7 ,wherein said locking/unlocking mechanism is unlocked when the rotationalspeed of said motor shaft is at a predetermined value or more.
 9. Avehicle according to claim 7 , wherein said locking/unlocking mechanismis unlocked when said first motor stops generation of a torque.
 10. Avehicle according to claim 7 , wherein said locking/unlocking mechanismis locked after the rotational speed of the motor shaft in thelocking/unlocking mechanism has been subjected to even speed control bysaid first motor.
 11. A vehicle according to claim 7 , further includinga failure detecting means for detecting a failure of saidlocking/unlocking mechanism, and a speed limiting means which limits thespeed of the vehicle or of the engine in accordance with a signalprovided from said failure detecting means.
 12. A vehicle according toclaim 7 , further including a failure detecting means for detecting afailure of said locking/unlocking mechanism, and a voltage suppressingmeans which suppresses a counter electromotive force of said first motorin accordance with a signal provided from said failure detecting means.